The role of red blood cells is to transport oxygen around the body. The oxygen-carrying capacity of red blood cells varies from species to species. The oxygen-carrying capacity depends partly on the size and structure of the red blood cells and their haemoglobin content. *(b) The table shows some information about red blood cells from four species of air- breathing mammals. The species are listed by decreasing size. Explain the relationships between the sizes of these species of mammal, the characteristics of their red blood cells and their oxygen-carrying capacity. Use the information in the table to support your answer. (6) ................................................................................................................................................................................................................................................................................ ................................................................................................................................................................................................................................................................................ ................................................................................................................................................................................................................................................................................ ................................................................................................................................................................................................................................................................................ ................................................................................................................................................................................................................................................................................ ................................................................................................................................................................................................................................................................................ ................................................................................................................................................................................................................................................................................ ................................................................................................................................................................................................................................................................................ ................................................................................................................................................................................................................................................................................ ................................................................................................................................................................................................................................................................................ ................................................................................................................................................................................................................................................................................

Answer:

Mean number of cells per \(\mathrm{dm}^{3}\) of blood
- no correlation with size of mammal / some indication that as size of mammal decreases the number increases, with the exception of camels

Mean mass of haemoglobin:
- some indication that mass of haemoglobin per cell decreases with size of mammal, with the exception of camels / man
- mammals with high numbers of red blood cells have lower mean mass of haemoglobin per cell / converse
- total mass of haemoglobin decreases with size of mammal
- because high number would partially compensate for less haemoglobin as the smaller mammal may require less energy
- so respiration would be less
- total mass of haemoglobin decreases with size of mammal

Mean cell volume:
- cell volume decreases with size of land mammals, except camels
- possibly because their blood vessels are narrower
- cell volume of camels is particularly large
- possibly because their blood vessels are wider
- as more heat needs to be lost in the hot temperatures

Oxygen-carrying capacity:
- oxygen carrying capacity of blood decreases with decrease in size of mammal
- oxygen-carrying capacity decreases with total mass of haemoglobin
- as the smaller mammal may require less energy
- so respiration would be less

Overall:
- these three factors determine the oxygen-carrying capacity of the blood
- but other factors would also affect oxygen-carrying capacity
- e.g. affinity of haemoglobin for oxygen
- beluga whales have relatively small cells but high mass of haemoglobin and high concentration enabling their high oxygen-carrying capacity
- as swimming takes a lot of energy
- as the water they live in is cold
- and energy is needed to keep warm
- therefore rate of respiration is high
- and the animals have to surface to acquire their oxygen from the air

Knowledge points:

Solution: